Multi-Circuit Heat Exchanger

ABSTRACT

The present invention relates to an exchanger comprising at least two circuits, this exchanger comprising:
         a series of tubes for the circulation of fluid of one or other of the two circuits,   at least two collector rings, each connected to the opposite ends of the tubes, said tubes opening respectively into said collector rings,   a partition provided in each of said collector rings defining at least one separation in order to isolate the first circuit from the second circuit of fluid,   a mechanical connection means connecting the structure of the inlet chamber to the collection chamber is designed to reduce significantly the structural mechanical stresses existing in the separation between the two circuits,
 
characterized in that the mechanical means consists in a total or partial closing off of at least one tube situated next to the partitions.

The present invention relates to a multicircuit exchanger.

More particularly, but not exclusively, its subject is an exchanger comprising at least two independent or partially independent circuits inside which at least two fluids which may or not be different circulate before being cooled by a circulation of external air.

It applies in particular to the multicircuit exchangers used in the automobile industry in order to cool two elements which have different cooling needs such as the heat engine and the gearbox for example.

It is particularly well suited to multicircuit exchangers used in the case of a hybrid engine in order to cool the electric motor on the one hand and the heat engine on the other hand.

For reasons of manufacturing cost and to make integration into the vehicle easier, it is preferable to perform the cooling functions of the two fluids in a multicircuit exchanger rather than in two separate exchangers. Conversely, it is imperative to thermally isolate the two circuits as much as possible by removing as much as possible the thermal stresses due to the differences in temperature between the two circuits. Specifically, the fluids circulating in the two separate circuits do not necessarily have the same cooling energy needs nor necessarily the same inlet and outlet temperatures. In order to optimize the operation and longevity of the exchanger, it is therefore important to minimize the thermal stresses.

Conventionally, exchangers comprises a series of thin light alloy cylindrical tubes, often of flattened shape leading into two collector rings. The seal between these tubes and the collector ring is provided by the interposition of elastic seals or by braising. Very thin light alloy interlocked strips folded in an accordion shape are inserted between the tubes in order to increase the contact area between the exchanger and the ambient air travelling between the tubes; these interlocked strips conventionally being called inserts.

Conventionally, multicircuit exchangers comprise a separating partition in the two collector rings in order to separate the two circuits. Unfortunately the structural elements close to this partition (mainly the thin tubes) do not withstand the mechanical stresses (particularly fatigue) due to the difference in temperature (particularly because of the temperature difference cycles) existing between the two circuits. The thinnest structures such as the tubes are the most susceptible to breakage and to generating leaks.

This situation is accentuated in the case of braised light alloy tubes to the extent that the heat treatments necessary for braising make the light alloy less rigid and more vulnerable to the creation of cracks originating from the thermal stresses particularly with respect to the bending or stretching stresses.

In order to attempt to remove these disadvantages, it has been proposed to increase the cross section of the partition or even to double it but the problem remains because the differential expansions between the hot tubes and the relatively cooler tubes still exist and create internal fatigue stresses that are too great.

Furthermore, it should be noted that the thermal stresses at the border between the two circuits are considerable when the thermal gradient existing at this location between the two circuits is great.

In order to remedy these major disadvantages, the invention departs from the architectures mentioned above and proposes an exchanger comprising at least two circuits, this exchanger comprising:

-   -   a series of tubes for the circulation of fluid of one or other         of the two circuits,     -   at least two collector rings, each connected to the opposite         ends of the tubes, said tubes opening respectively into said         collector rings,     -   a partition provided in each of said collector rings defining at         least one separation in order to isolate the first circuit from         the second circuit of fluid,     -   a mechanical connection means connecting the structure of the         inlet chamber to the collection chamber is designed to reduce         significantly the structural mechanical stresses existing in the         separation between the two circuits.

According to the invention, this exchanger is characterized in that the mechanical means consists in a total or partial closing off of at least one tube situated next to the partitions.

The abovementioned mechanical stresses arise from the differential expansions of the heat-exchange tubes generated by the differences in temperature between the two circuits.

“Separation” means an imaginary line connecting the two partitions that are present respectively in each of the collector rings and that mark the boundary or limit between each of the two circuits. In a conventional manner, this separation consists in a straight line or a plane extending in the plane of extension or in the axis of the tubes and/or of the partitions.

In nonlimiting embodiments, the multicircuit exchanger according to the invention can have additional elements and/or features described below taken in isolation or in combination:

-   -   the mechanical connection element consists in a brace.     -   the brace, or mechanical means, is immediately next to a fluid         circulation tube that is closest to the separation.     -   the mechanical connection element mechanically connecting the         two collector rings is placed between two adjacent tubes of the         two circuits.     -   the mechanical connection element or brace mechanically         connecting the two collector rings is placed in a region of the         exchanger in which the temperature and therefore expansion is at         an intermediate level between those of the two circuits.     -   the mechanical connection element mechanically connecting the         two collector rings consists of at least two solid or hollow         bars or braces placed on each side of the separation partition         existing between the distribution chambers.     -   the mechanical connection element or brace consists in an         extension of the partitions separating said chambers.     -   the mechanical connection element or brace consists of a tube         identical to the other heat-exchange tubes but in which no fluid         circulates.     -   the mechanical connection element or brace consists of at least         one heat-exchange tube identical to the other heat-exchange         tubes but having a fluid inlet and/or outlet orifice that is         restricted in order to limit the flow rate of fluid.     -   the mechanical connection element or brace consists of at least         one heat-exchange tube identical to the other heat-exchange         tubes but having a wall thickness that is greater at least in         one zone situated close to the fluid inlet and/or outlet orifice         in order to limit the flow rate of fluid and to mechanically         reinforce at least locally the connection element.     -   the mechanical connection element or brace consists of several         tubes identical to the other heat-exchange tubes but in which no         fluid circulates, these tubes being placed on either side of the         wall separating the two circuits.     -   the exchanger is completely mechanically assembled by crimping         with no braising.     -   the separation partition separating the two circuits comprises a         small orifice allowing the fluid to travel from one circuit to         the other.     -   the multicircuit exchanger consists mainly of an aluminum alloy         and is assembled by braising.     -   the multicircuit exchanger may comprise boxes produced by         injection of plastics, these boxes being assembled to the         collector rings by crimping.

Embodiments of the invention will be described below as nonlimiting examples, making reference to the appended drawings in which:

FIG. 1 is a schematic cross section of a multicircuit exchanger with two independent circuits according to the prior art.

FIG. 2 shows schematically an exemplary embodiment of an exchanger with two independent circuits according to the invention.

FIGS. 3 to 8 are variant embodiments of an exchanger with two independent circuits according to the invention also in schematic cross section.

In the rest of the description, the expression “mechanical means” will be used to define in a general manner the subject of the invention. Nevertheless, it is clear that this expression can also be reflected in the term “brace”, in particular in order to mark the fact that this mechanical means connects the two collector boxes.

FIG. 1 shows an exchanger 1 with two independent circuits as is conventionally produced according to the prior art. It comprises a first circuit A inside which a first fluid circulates and a circuit B inside which a second fluid circulates. This exchanger comprises two collector rings C1 and C2 responsible for collecting the fluid. These collector rings are each separated in two portions by a wall P1 and P2. A set of tubes (in this instance numbering 7) t1 to t7 connect the two collector rings. Thin interlocked strips made of aluminum alloy folded in the shape of an accordion are inserted between the tubes to increase the area of contact between the tubes and the surrounding air. Each circuit comprise an inlet and an outlet. The fluid of the circuit A enters the circuit via the inlet Ea and leaves via the outlet Sa after having circulated in the tubes t1, t2, t3, t4. The fluid of the circuit B enters the circuit via the inlet Eb and leaves via the outlet Sb after having circulated in the tubes t5, t6, and t7. If the average temperature of the first fluid in the circuit A is higher than the average temperature of the second fluid of the circuit B, then the tubes t1 to t4 are hotter than the tubes t5 to t7. In this case, the tubes t1 to t5 tend to expand more than the tubes t5 to t7. The result of this is compression and bending stresses in the tubes t1 to t4 and stretching and bending stresses in the tubes t5 to t7. Because of the extremely hyperstatic aspect of the tube/collector rings mechanical attachment, it is the tube t5 and the structure close to the end of this tube t5 which is most subjected to the risk of developing a crack by the fatigue effect of alternating stretching/bending stress.

In the nonlimiting exemplary embodiments illustrated in FIGS. 2 to 8, the exchanger mainly comprises

-   -   two independent circuits A and B, a collector ring C1 which is         separated into two independent portions by a wall P1,     -   a second collector ring C2 which is also separated into two         independent portions by a wall P2,     -   three tubes t1, t2, and t3 which connect in a sealed manner the         collector ring C1 to the collector ring C2 and which allow the         first fluid of the circuit A to circulate from an inlet Ea to an         outlet Sa,     -   three tubes t5, t6, and t7 which connect in a sealed manner the         collector ring C1 to the collector ring C2, and which allow the         second fluid of the circuit B to circulate from an inlet Eb to         an outlet Sb,     -   thin strips of light alloy folded in the shape of an accordion         which are inserted between the tubes to increase the area of         contact between the tubes and the surrounding air,     -   a mechanical connection S which mechanically connects the two         collector rings.

In a third exemplary embodiment according to the invention illustrated in FIG. 2, the mechanical connection S consists of a tube t4 made of light alloy. For the purpose of uniformity, and to reduce the manufacturing cost, this type of tube is similar to the tubes used for the circulation of fluid. However, in the tube t4 used as an additional structure, no fluid circulates. To prevent any circulation of fluid in this tube, one or two stopper(s) 3 close(s) off one or both end(s) of the tube t4. Here again, since the tube t4 is not supplied with a fluid, it is at an intermediate temperature which somewhat reduces the stresses due to the temperature differences that exist between the two circuits.

In a fourth exemplary embodiment according to the invention illustrated in FIG. 3, the mechanical connection S, or brace, consists of two tubes t3 and t4 made of light alloy. These two tubes are closed off at one or both of their ends and therefore, as in the preceding example, are not traversed by the fluids. Here again, since the tubes t3 and t4 are not supplied with a fluid, they are at an intermediate temperature which somewhat reduces the stresses due to the temperature differences that exist between the two circuits.

In a fifth exemplary embodiment according to the invention illustrated in FIG. 4, the mechanical connection S consists of two tubes t4 and t5 made of light alloy. These two tubes are closed off at one or both of their ends and therefore, as in the preceding example, are not traversed by the fluids. Here again, since the tubes t4 and t5 are not supplied with a fluid, they are at an intermediate temperature which somewhat reduces the stresses due to the temperature differences that exist between the two circuits.

In a sixth exemplary embodiment according to the invention illustrated in FIG. 5, the mechanical connection S consists of four tubes t3, t4, t5 and t6 made of light alloy. These four tubes are closed off at one or both of their ends and therefore, as in the preceding example, are not traversed by the fluids. Here again, since the tubes t4, t5, t6, and t7 are not supplied with a fluid, they are at an intermediate temperature which somewhat reduces the stresses due to the temperature differences that exist between the two circuits.

In a seventh exemplary embodiment according to the invention illustrated in FIG. 6, the mechanical connection S consists of a tube t4 made of light alloy. This tube is partially closed off and is traversed by the fluid but with a weaker flow rate. The influence of such a tube on the structural stresses is therefore less than if it was a tube that was completely closed off but all the same makes it possible to somewhat reduce the stresses due to the temperature differences that exist between the two circuits.

In a sixth exemplary embodiment according to the invention illustrated in FIG. 6, the mechanical connection S consists of two tubes t3 and t4 made of light alloy. These tubes are partially closed off and are traversed by the fluid but with a weaker flow rate. The influence of such tubes on the structural stresses is therefore weaker than if they were tubes that were completely closed off, but all the same makes it possible to somewhat reduce the stresses due to the temperature differences that exist between the two circuits.

In a ninth exemplary embodiment according to the invention illustrated in FIG. 8, the mechanical connection S consists of three tubes t3, t4 and t5 made of light alloy. These tubes are partially closed off and are traversed by the fluid but with a weaker flow rate. The influence of such tubes on the structural stresses is therefore weaker than if they were tubes that were completely closed off but makes it possible all the same to somewhat reduce the stresses due to the temperature differences that exist between the two circuits.

In an eighth exemplary embodiment according to the invention illustrated in FIG. 9, the mechanical connection S consists of a metal plate P, in this instance made of light alloy, which passes completely through the exchanger 1. This plate P is braised to the periphery of each collector ring in order to ensure the seal between the two circuits, and therefore forms a rigid link between the two collector rings. Thus this plate P is at an intermediate temperature which reduces the stresses due to the temperature differences that exist between the two circuits. This plate may advantageously be replaced by a hollow plate (FIG. 10).

Those skilled in the art will be able to apply this concept to many other similar systems without departing from the context of the invention defined in the attached claims. 

1. An exchanger (1) comprising at least two circuits (A) and (B), said exchanger (1) comprising: a series of tubes for the circulation of fluid of one or other of the two circuits (A) or (B), at least two collector rings, each connected to the opposite ends of said tubes, said tubes opening respectively into said collector rings, a partition (P1 and P2) provided in each of said collector rings defining at least one separation in order to isolate the first circuit (A) from the second circuit (B) of fluid, a mechanical connection means (S) connecting the structure of an inlet chamber to a collection chamber which reduces the structural mechanical stresses existing in the separation between the two circuits (A and B), characterized in that said mechanical connection means (S) totally or partially closes off of at least one tube situated next to said partitions (P1) and (P2).
 2. An exchanger (1) according to claim 1, characterized in that said mechanical connection means (S) comprises a brace.
 3. An exchanger (1) according to claim 1, characterized in that said mechanical connection means (S) is immediately next to a tube that is closest to the separation.
 4. An exchanger (1) according to claim 1, characterized in that said mechanical connection means (S) mechanically connecting said two collector rings is placed between two adjacent tubes of the two circuits (A and B).
 5. An exchanger (1) according to claim 1, characterized in that said mechanical connection means (S) mechanically connecting said two collector rings is placed in a region of said exchanger (1) in which the temperature and therefore expansion is at an intermediate level between those of the two circuits (A and B).
 6. An exchanger (1) according to claim 1, characterized in that said mechanical connection means (S) mechanically connecting said two collector rings comprises at least two solid or hollow bars or braces placed on each side of said partition existing between said chambers.
 7. An exchanger (1) according to claim 1, characterized in that said mechanical connection means (S) comprises an extension of said partitions separating said chambers.
 8. An exchanger (1) according to claims claim 1, characterized in that said mechanical connection means (S) comprises a tube identical to said other tubes but in which no fluid circulates.
 9. An exchanger (1) according to claim 1, characterized in that said mechanical connection means (S) comprises at least one tube identical to said other tubes but having a fluid inlet and/or outlet orifice that is restricted in order to limit the flow rate of fluid.
 10. An exchanger (1) according to claim 1, characterized in that said mechanical connection means (S) comprises at least one tube identical to said other tubes but having a wall thickness that is greater at least in one zone situated close to a fluid inlet and/or outlet orifice in order to limit the flow rate of fluid and to mechanically reinforce at least locally said mechanical connection means (S).
 11. An exchanger (1) according to claim 1, characterized in that said mechanical connection means (S) comprises several tubes identical to said other tubes but in which no fluid circulates, said several tubes being placed on either side of said partition separating the two circuits (A and B).
 12. An exchanger (1) according to claim 1, characterized in that said exchanger (1) is completely mechanically assembled by crimping with no braising.
 13. An exchanger (1) according to claim 1, characterized in that said partition separating the two circuits (A and B) comprises an orifice allowing the fluid to travel from one circuit to the other.
 14. An exchanger (1) according to claim 2, characterized in that said brace is immediately next to a tube that is closest to the separation. 